Outbreak in Sierra Leone Is Tied to Single Funeral Where 14 Women Were Infected

Sierra Leone’s explosion of Ebola cases in early summer appears to stem from one traditional healer’s funeral at which 14 women were infected, according to scientists studying the blood of victims.

The funeral, which took place in mid-May, constitutes a “super-spreader” event comparable to one in 2003 in a Hong Kong hotel in which one doctor from China dying of SARS infected nine other guests who spread the virus throughout the city and to Vietnam and Canada.

The funeral was in Koindu, a diamond-mining town across the border from Guéckédou in Guinea, where the outbreak is thought to have begun in December, and the healer was known for treating victims of a mysterious illness that turned out to be Ebola.

The funeral’s central role, which local doctors had anecdotally suspected, was confirmed by geneticists at the Broad Institute of M.I.T. and Harvard who sequenced the virus found in 78 patients treated at Kenema Government Hospital in northeastern Sierra Leone, near the borders with Liberia and Guinea, two countries that are also at the heart of the outbreak.

“It’s frightening that a single event could catalyze a whole outbreak, but that’s what it looks like happened,” said Dr. W. Ian Lipkin, a renowned virus hunter at Columbia University, who called the study “a really nice piece of work.”

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Dr. Sheik Humarr Khan, Sierra Leone’s leading hemorrhagic fever expert, died from Ebola along with four of his other co-authors before the study was published.CreditPardis C. Sabeti

The scientists not only found that all 78 had virus traceable to funeral guests, but also showed that the West African Ebola strain was quite different from a strain that has been circulating thousands of miles away in Central Africa since 1976, and that the two probably diverged as far back as 2004.

“No one knows where it’s been during that time,” said Dr. Pardis C. Sabeti, a Harvard geneticist and study co-author.

It might, she added, have circulated in some combination of bats, apes or other forest animals, “or it could have been circulating in humans for 10 years with little or no notice.”

That information is important, experts said, because the diagnostic tests now in use, as well as drugs and vaccines under consideration, are based on the Central African strain and might not work well on this outbreak. For example, a diagnostic test in use now might not give a clear positive if a victim had a low viral load early in an infection.

The study also found that the 78 victims had two variants of the West African strain. The healer might have been infected with two variants from two of her patients, said Stephen K. Gire, another co-author from Dr. Sabeti’s lab. Or someone else at the funeral could have been infectious.

The work had a sobering footnote: Before it could be published, five of its co-authors died of Ebola. They included Dr. Sheik Humarr Khan, Sierra Leone’s leading hemorrhagic fever expert, and four other staff members at the Kenema hospital. By midsummer, so many hospital staff members and patients had died that it was considered a death trap and partly vacated.

Since that note was written, Dr. Sabeti said, a sixth co-author, also at the hospital, died of a stroke.

“They’re such amazing heroes, dealing with an unfathomable situation,” she said. “When we heard Khan had Ebola, I was all, ‘We’ve got to do this, we’ve got to do that.’ And then my face kind of melted, and I began bawling. And I turned to the room, and everyone began bawling.”

It’s not known why only they became infected. Women normally wash the bodies, “but at a traditional burial, presumably everyone had some interaction with the body,” Dr. Garry said.

(Several scientists, including Dr. Sabeti, complained that many Westerners describe African funeral rites as bizarre, when it is actually routine around the world to wash and dress corpses — though in wealthy countries, undertakers are paid to do it. In many countries, including the United States, it is not uncommon for mourners to touch or kiss a loved one in an open coffin.)

Dr. Garry’s team began collecting blood after one woman who had attended came to the Kenema hospital with a high fever that had begun May 25; the exact date of the funeral was vague, but the typical incubation period is eight to 10 days.

The Kenema hospital was ready to ship samples because it collaborates with foreign laboratories to study Lassa fever. Lassa is unrelated to Ebola but can also cause fatal bleeding. If Ebola circulated for years, some deaths could have been misdiagnosed as Lassa or typhoid or malaria, which all have similar early symptoms.

Because the hospital is still overwhelmed and now overseen by the World Health Organization, Dr. Sabeti said, she has received no samples since June.

To help researchers working on drugs or vaccines, she has been posting sequences as soon as she has them, rather than waiting until academic journals publish her papers.

“It doesn’t take a village to fight this,” she said. “It takes a planet.”

A version of this article appears in print on , on Page A7 of the New York edition with the headline: Outbreak in Sierra Leone Is Tied to Single Funeral Where 14 Women Were Infected. Order Reprints | Today’s Paper | Subscribe